1. Field of the Invention
The present invention relates to apparatus for controlling liquid flow, for example to a dosing apparatus for filling liquids into containers.
2. Description of the Prior Art
U.S. Pat. No. 2,399,300 discloses a filling apparatus including a supply line and a valve therein responsive to pressure in the line for shutting off the line when the line pressure falls below a certain minimum. The supply line leads from a source of liquid to a rotary filler tank equipped with filler heads. A regulatable source of vacuum is connected through a pipe and a swivel joint into the top of the tank. The valve comprises a casing formed with a conical seat with which diametrically opposed, fixed, inlet and outlet ports are in communication. A valve plug cooperating with the seat is equipped with an operating handle. The plug has a diametric passage including an enlarged middle section. At one end the enlargement is formed as a seat with which is co-operable a valve closure member of a check valve mounted in the enlargement. The closure member is equipped with a stem which is guided in a spider at the opposite end of the enlargement from the closure member. A compression spring encircling the stem and interposed between the spider and the valve closure member acts to seat the latter. Of the two side walls of the plug between the closure member and the spider, one is solid, whereas the other is formed with an opening communicating with immediately downstream of the closure member. Depending upon the position of the plug as set using the handle, the one side wall positively cuts off the supply line; or the check valve is placed in control of flow through the supply line; or the opening communicates with the fixed inlet port, so that the check valve is by-passed and the supply line is drained into the tank. When the check valve is in control, it serves to differentiate between fluids of different specific gravity; for example between milk and air. The vacuum effect is of itself incapable of unseating the check valve, such action being possible only as a result of the total pressure of the liquid acting on the check valve.
U.S. Pat. No. 4,254,806 discloses an apparatus for filling caulking tubes in a clean manner with a liquid viscous composition, wherein to a nozzle from which the composition passes into the tube there is connected a suck-back means comprising a first piston-and-cylinder device which retracts away from the nozzle when composition is not being forced into the tube, so as to create suction upon the composition in the nozzle and thus prevent it leaking from the nozzle. The first piston-and-cylinder device is operable via a four-way valve via which is also operable a second piston-and-cylinder device which turns a rotary valve having first, second and third fixed ports and first and second rotary ports. The first fixed port is an inlet for the caulking composition, the second fixed port communicates with a metering piston-and-cylinder device for the composition and the third fixed port is an outlet to the nozzle. The rotary valve is a two-position valve in one position of which the inlet port is connected via the rotary ports with the second fixed port and in the other position of which the second fixed port is connected via the rotary ports with the outlet port. This apparatus is not suitable for handling fluids of differing characteristics, particularly viscosities. Firstly, the resistance to fluid flow of the path from the metering cylinder to the nozzle outlet is the same irrespective of the viscosity of the fluid. Secondly, the stroke of the suck-back means is not adjustable in order to adjust the vacuum produced thereby to the fluid to be filled.
The apparatus disclosed in European Patent Specification No. 0138234 has been designed with a view to coping with filling liquids of differing viscosities. It comprises a filler tank from which extend downwards filler heads connected by branch conduits to respective metering cylinders and terminating in outlet nozzles. Two kinds of outlet nozzles are selectively mountable at the end of each filler head; one for high viscosity liquid and the other for low viscosity liquid. The high-viscosity liquid nozzle comprises a tubular nozzle main body attachable to the filler head, a damper pivoted to the lower end of that body, a damper opening rod vertically movably supported by that body, and a spring for biasing the rod upward. The low viscosity liquid nozzle comprises a tubular nozzle main body, a lower check valve in the upper end of that body, and a metal net disposed in the lower end of that body. Not only are these two nozzles rather complicated, but also the changing of them is time-consuming.